Technical Field
The technology relates to methods and structures for calibrating test channels of automated test equipment (ATE).
Discussion of the Related Art
Referring to FIG. 1, a conventional ATE system 100 (sometimes referred to as a “tester” or an “ATE”) may comprise an automated tester 110 having a plurality of test channels (not shown) that have contacts forming a tester interface 131. Each channel can each generate or measure a signal at a channel contact, which may be connected to a test point on a device under test 150 through a device interface board 135.
Within the tester 110, the test signals may be generated or measured in instruments. Each instrument may process signals for multiple channels, such that each instrument is coupled to multiple contacts at tester interface 131. Frequently, the contacts for each instrument are close together in tester interface 131. For example, a typical contact density would entail multiple regions, each about one square inch, having a large number of contacts, such as 64.
In some implementations, the device under test 150 may be a wafer or one or more packaged integrated circuits. For example, the ATE may be used for testing integrated circuit devices on a wafer for quality assurance prior to dicing the wafer and packaging the devices.
Because integrated circuit devices are typically manufactured in large quantities on a wafer and may be operated at high speeds (e.g., data rates up to and greater than 10 Gb/s), an automated tester 110 may have hundreds or thousands of channels. Each channel, itself, must operate at a high speed with high timing accuracy and high accuracy in measuring voltages or other parameters. To achieve the required accuracy, each channel is calibrated or verified from time to time.
In a conventional calibration procedure, calibration may be achieved by removing the device interface board 135 to expose the tester interface 131. The device interface board 135 may be replaced by a robot assembly with a single probe connected to a signal analyzer through a short coax cable. The robot may move the probe from one channel to another during the calibration process. Such connections made through a coaxial cable provide high signal fidelity at the instrument used for calibration measurements, ensuring that the measurements have the accuracy required for accurate calibration of tester channels.